OK, this is now implemented -- the list by tag page has feeds specific to each tab (sort). You can find them linked at the bottom of the page, like all our other feeds.
They are labelled appropriately:
The highest voted is a little odd since it will be extremely static -- you'll get the top 30 voted questions in those tag(s), which isn't likely to change much over time. It makes sense as browse order but as a top (n) rss feed I think we need a time interval specified there as well, or something. Of course doing that would make it very similar to the "hot" rss, too, so.. hm.
1 this was the only tag based feed available before so the syntax is identical.